The technology for producing integrated circuits ("ICs") continues to rapidly advance resulting in increasing circuit miniaturization and an increasing number of devices per chip ("chip density"). These devices commonly require steady current and voltage sources in order to operate effectively.
In certain prior art devices, constant reference voltages and currents are provided to devices on the IC through use of an external voltage source and an external precision resistor to supply a current to a reference circuit on the IC, which subsequently provides a constant current for each of the devices on the IC. The ideal result is steady voltages and currents supplied to each and every device within the IC that are equal to precisely the voltages and currents required by each one of these devices.
One problem with such a configuration is that with the currently available processes utilized to produce integrated circuits, such as with MOS technology, processing variations result in inconsistencies between devices located on different areas of the same IC. Thus, a reference circuit produced on one part of the IC may end up supplying different current and voltage magnitudes to different portions of the IC because of variations within the IC structure that result from the particular process that produced the IC. Furthermore, as the chip density increases and the devices become smaller and smaller, processing variations become a greater factor in the operation of the devices in conjunction with each other.
Other factors that may result in variations across the same IC are the different processes utilized to construct the different layers, or sections, of the IC (e.g. evaporation, deposition, etc.), differing angles within the wafer and the differing temperatures utilized in the various processes.
A separate problem that may arise is chip noise. Often, the major implementation within the IC is for digital circuitry, which commonly generates an immense amount of noise. The reference circuits utilized within the IC are analog circuits which require power supplies which are very quiet. Thus, noise from the digital circuitry often interferes with the function of the analog circuits constructed on the same chip.
The above problems are compounded within the implementation of a digital to analog circuit ("DAC"), since a DAC requires a plurality of energy (commonly, current) sources that produce the analog signal that is outputted from the DAC. Precision within the DAC is necessary so that the outputted analog signal is uniform and smooth throughout the digital to analog conversion process. Thus, it is necessary that the various energy sources utilized throughout the DAC and located throughout the IC on which the DAC is implemented are supplied with steady and uniform reference voltages and currents. In other words, an energy source residing in one portion of the DAC must be supplied with the same reference voltages and currents as are supplied to an energy source in another "distant" portion of the DAC.
Thus, there is a need for an implementation of reference voltage and current sources within an IC that are able to supply stable and uniform reference voltages and currents to all portions of the IC despite process variations within the IC.
There is also a need for a reference source within an IC that is immune to the noise produced by digital circuitry within the IC.
There is yet a further need for steady uniform reference voltages and currents to be supplied to all energy sources within a DAC.